Magnets using relatively inexpensive ferrite (iron-base oxide) (i.e. ferrite magnets) have heretofore been utilized for various products in different fields. In recent years, ferrite magnets requiring no rare metal, such as rare earth magnets, come to the front from the view point of resources aspect.
Ferrite as a magnetic material, which is the collective term for ceramics containing iron oxide (Fe2O3) as main component, falls into the general classification of a cubic system, such as spinel-type ferrite (referred to as “S-type ferrite” hereinafter) used for a soft magnet, and a hexagonal system, such as M-type ferrite used for a hard magnet (permanent magnet). Among them, notable one is the latter hexagonal ferrite to be a hard magnet.
Hexagonal ferrite comprises AO-M2+O—Fe2O3 (A: Ba, Sr, etc/M: Zn, Cu, etc), and there may exist plural types, such as M-type, W-type, X-type, Y-type, and Z-type, in accordance with the combination of specific metal elements. Actually focused ones as materials for permanent magnets are, however, only the M-type ferrite and the W-type ferrite. Particularly, almost all ferrite magnets utilized at the moment are the M-type ferrites, such as SrO 6Fe2O3 and BaO 6Fe2O3. In contrast, the W-type ferrite has scarcely ever been put to practical use.
However, the W-type ferrite has higher saturation magnetization than that of the M-type ferrite. Accordingly, if allowed for taking advantage of W-type ferrite, a ferrite permanent magnet with higher magnetic characteristics than conventional ones would be obtained. From such viewpoints, various proposals for W-type ferrite and magnets employing the same have been made, which include the descriptions relevant to the following patent literatures, for example.